1. Field of the Invention
The present invention relates to an image sensor, which detects radiation, and to a method of manufacturing image sensors.
2. Description of the Related Art
An image sensor, which detects radiation such as hard X-rays or γ-rays so as to generate image information, has been used in various technical fields. For example, a radiant field from a certain celestial body is detected, and thereby, it is possible to know the physical status of the celestial body and the spatial structure thereof. Further, X-rays are irradiated to a human body, and then, the transmitted wave is investigated, and thereby, tomography of the human body can be obtained. Besides, the image sensors have also been used in other fields, such as nuclear power (glass solidification check of radioactive waste, radiation monitor, etc.), non-destructive tests (semiconductor tester, etc.) and mineral surveying (mineral resources research).
The image sensor conventionally used for the above fields has the following structure, for example.
FIG. 1A is a view showing a typical example of the above conventional image sensor 80, and FIG. 1B is a cross-sectional view taken along the B—B direction of FIG. 1A. As shown in FIG. 1A and FIG. 1B, the image sensor 80 has a detecting element (Si element or Ge element) 81, and an amplifying IC 84. More specifically, the detecting element 81 detects incident radiation so as to generate an electric signal. The amplifying IC 84 is arranged on the same plane as the detecting element 81, and amplifies the electric signal. In the image sensor 80, an interconnection line 83 led out of the detecting element 81 is connected to the amplifying IC 84 by wire bonding.
In general, according to the above structure in which the detecting element and the amplifying IC are arranged on the same plane and mutually connected, it is difficult to greatly increase the number of the detecting elements 81 of the image sensor. The reason is because it is technically difficult to further lead many signal lines out of the peripheral region of the detecting element 81 by wire bonding.
The image sensor using the Si element detects only X-rays having a low energy from several KeV to tens of KeV; for this reason, the image sensor does not have the sensitivity required for practical use.
As typified by the CCD, the recent visible sensor technique has been specialized in slowly reading two-dimensional information under the condition that a signal to noise ratio is very good. However, in photons other than the visible light region, environmental noise is high and signals are weak; for this reason, high-speed operation and high-reduction of noise are required as not so compared with the case of detecting the visible light. As a result, there is a need of connecting a read circuit to each one of fine pixels, and the development of a high-speed parallel readable system has been required.
It has been known that silicon becomes transparent with respect to hard X-rays or γ-rays having a wavelength shorter than soft X-rays. Therefore, in order to obtain the large stopping power, the development of a new CdTe semiconductor must progress quickly.
The present invention has been made in view of the above circumstances. Accordingly, it is an object to provide a highly sensitive image sensor, which can readily make an electric connection between each sensor element and an amplifying IC even if it has many sensor elements, and to provide a method of manufacturing the image sensor.